Spectrum analysis apparatus



April 29, 1969 J. F. FRAZER ET AL 3,441,850

SPECTRUM ANALYSISAPPARATUS April 29, w69 J. F. FRAZER ET A1. 3,441,850

SPECTRUM ANALYSIS APPARATUS SheerI g! of 7 Filed Feb. 18, 1966 TIMERECORD ERASE PLAYBACK FIG.V lo

VOLTAGE Filed Feb. 18,

J. F. FRAZER ET AL SPECTRUM ANALYSIS APPARATUS Sheet lll /0 35 332;mllllllllll l lllllllll l! :I T I ff 742 77 37 6 f) I ZZIIIIIIIII IIIIIIIImIIIIIII I IIIIIMIIIII IIIIIIII IIIII'In'IHIIIIIIIIIIIm 511mm ImmCOMPARE CIRCUIT I PAST v I 7/- UP/DOI/I/N 4f MOTOR [UIIIIIIII I H! VCO/67 54 75- BRAKE DRIVE I/ /I DISC.

L ,g .63 L. SIAE SIILIIOSL E SWITCH GENERATOR OSCILLATOR I TVIBAG A 45 5If 76 7 22 I INPUT n REF. VOLTS -w ANIPL. MIXER Y l L 2 ISEGS I L L OR 5TIMES .M

DRUM SYNCHRONIZING CONTROL PANEL CLUTCH CIRCUIT 6/6 REC A STOP RII@ IIII II m6 CLUTCH /60 COIL 36A ff' l l Q T: 77z 46,) PL \W SPEED SELECTOR4?/ CONTOUR SELECTOR F G. Q

WJLl/rWQ/IZ/-MJ/ *'z/QEJ Affe/016].;

APM 29, m69 J. F. PRAZER ET AL 3,441,850

SPECTRUM ANALYSIS APPARATUS Filed Feb. 1S, 1965 sheet 4 of 7 PROMPLAYSACK HEAO PLAYBACK SPEAKER PRE-AMP AMP AMP 57 64 PROM v C O nSALANCED Ul V C0 DRVE 455 TO 555 KC MODOLATOR D V M FILTER /W 65 PROMDGTAL EOO 50o OR VCO DRIVE READOUT |500 CPS im BANOWIOTH /5 75 IF VIDEOMARK /9 GENERATOR A TO O A FREQUENCY 9 CONVERTER MARK SIGNAL Y Y /50FROM T VIDEO CONTOUR CON OUR SELECTOR z GENERATOR SHAPER 24 TO STYLUSCONTROL z -m b E SWITCH SILT April 29, 1969 1. F. FRAZER ET AL 3,441,850

SPECTRUM ANALYSIS APPARATUS FilIed Feb. 18, 1966 Sheet 5 of 7 AMPUHERCROSSOVER 54 C X 8 OETECTOR T DIGITAL TO ANALOG VIDEO CONVERTER FROMCROSSOVER L )EMOOULATOR DETECTOR 55 5g 9/ 55) CLOCK 5P' SWITCH f- FLPBNARY PULSE FLOP COUNTER GENERATOR LOGIC 9 I l MATRIX 90 CONTOURyPIJLSES TO VIDEO SHAPER CONTOLIR LOC/IRITHNIIC DECIMAL SINARY N I S O OI O O O O 2 I5 O O I I I I O 3 3o O I I I I O O 5@ 4 a O O I o O O I F 5I5 O O I I I I S SO O I I I I O I 7 C3 I I I I I I 1 21 S4 STEPSTAIRCASE 9 WAVEFORM LUO) 9 2@ I E IS. T @SEI m I O LD EAI ZI I O: @C

2 C3 Om/Ju/v /av-(f Atorne):

April 29, 1969 J, F, FRAZER ET AL 3,441,850

SPECTRUM ANALYS I S APPARATUS Filed Feb. 18, 1966 sheet 6 of '7 7 I e g5J E 2 -5 E f 4 E E q l 2 O O f Tl TIME-w FB 9 I i IMI IWI!! Ul III lIIHIII TIIvIE TIME- i G. 9D

FROM RECORD /0/ FROM SWITCH Oc. PLAYBACK o SWITCH UNLATCH I AT H SWITCHC /Oo RSUYIFSCES /05 ,UNLATCH RESET I UNLATCH SWITCH COUNTER CLUTCHLATCH RELAY X/O I /04 Q05 5A I ATCH 5 FLIP fWA FLOR AHRE g2 FROIvI PHOTOCEEI.

pli 29, 1969 J. F. FRAZER ET AL 3,441,850

SPECTRUM ANALYS IS APPARATUS Filed Feb. 18, 1966 Sheet 7 of '7 PIN GEARMEMORY OISK ANGLES IN RAOIANS TIMING POSITION POSITION OF ENO NUMBER OFPULSES OP PIN OF MESSAGE IN OOUNTER START OE PLAYBAOK e n o PHOTOOELLPULSE w 17+2l12Tr-e+@] 2[2TT-e+d2] i203@ SYNOIIRONIZATION mme-@I 712I2TFG+Q1+4IO0I I0,000

COMPLETE OR OR 269-@ ITT I7+2e -245 I0,000

United States Patent "ice 3,441,850 SPECTRUM ANALYSIS APPARATUS .lohn F.Frazer, Lexington, Richard Holzman, Framingham, Kenton I. Ide, Lincoln,and Richard K. Moore, South Weymouth, Mass., assgnors, by mesneassignments, to Signatection, Inc., Waltham, Mass., a corporation ofMassachusetts Filed Feb. 18, 1966, Ser. No. 528,433 Int. Cl. G01r 23/18,13/02 U.S. Cl. 324-77 3 Claims ABSTRACT OF THE DISCLOSURE In aspectrograph for visually representing the analysis of a complex wave,amplitude is represented by spaced gradations, and discrete levels ofamplitude are further shown as contour lines.

This invention relates in general to the analysis of complex waves. Moreparticularly, the invention pertains to improved apparatus for depictingcomplex waves in a manner showing the variation in time of thedistribution of the energy in the complex waves over a selected portionof the frequency spectrum.

In analyzing complex waves of the type produced by music, speech, andother sounds, it has been conventional to transform the complex wavesinto a spectrograph in which amplitude variations of the frequencycomponents are represented by variations in the shade of thespectrograph pattern. That is, it is known that complex waves can beanalyzed by using those waves to produce a visual pattern of tones orshades upon a surface on which frequency is plotted along one axis andtime is plotted along another axis. The variation with time of theamplitude at the various frequencies is conveyed by the shades of thepattern, much as elevations in a topographical map of a geographicalarea are conveyed by color hues. Apparatus for representing complexwaves as a pattern of shade is disclosed in U.S. Patent No. 2,403,997.

Another method of visually representing complex waves is disclosed inU.S. Patent No. 2,425,003. Rather than employing gradations in shade toconvey variat-ions Iin wave amplitude at various frequencies, contourlines are used to mark discrete amplitude levels. Contour lines areuseful in that they permit more accurate quantitative determination ofthe wave energy distribution. The contour lines form a pattern of zonesand the amplitude represented by any point in a zone is somewherebetween the amplitude levels of the contour lines bounding that zone. Acon-tour line pattern can, however, be confusing because valleys andpeaks tend to look alike. That iS, care must be exercised to determinewhether the contour lines mark rises or falls in amplitude as all zonesare of the same shade or color.

The principal objective of the invention is to provide improvedapparatus for analyzing complex waves and for presenting the analysis inthe form of a chart showing the time variation in the distribution ofthe wave energy over a selected portion of the frequency spectrum. Inaccordance with the invention, the variation with time of the amplitudeof the frequency components is conveyed by gradations in tone of thepattern and contour lines are employed on the chart to mark discreteamplitude levels.

In the invention, the chart is generated upon a drum that isrepetitively encircled by a rotating stylus. The drum is translatedslowly upon i-ts axis, causing the stylus to trace a tightly coiledhelical path upon the chart. The stylus, during the generation of thechart, rotates in synchronism with a memory disk upon which the message4to 3,441,850 Patented Apr. 29, 1969 be analyzed has been recorded. Aportion of the recording track of the memory disk remains unused and thechart has a seam which is not written upon. A synchronization system isemployed in the invention to insure that the stylus passes over the seamat the time that the blank portion of the recording track is beingscanned by a playback head.

Additional improvements in the invention reside in the manner ofdetermining the discrete amplitude levels of the contour lines and inthe manner of digitizing the video signal to obtain a scale expansionfor low level video signals. The discrete amplitude levels aredetermined by a logic switching matrix which receives its input from abinary counter. The logic matrix is arranged to emit a signal wheneverthe outpu-t of the binary counter attains a count corresponding to acontour line amplitude level. A digital to analog converter responds tosignals from the counter by generating a staircase waveform whose stepsare the voltage equivalents of the counts in the counter. The videosignal is compared with the stairlcase waveform in a detector whichemits a pulse when the amplitude of the staircase waveform reaches theamplitude of the video signal. Where the occurrence of that pulsecoincides with a signal from the logic matrix, the stylus is energizedto mark a contour upon the chart. In effect the video signal isrepetitively compared with a staircase waveform and a contour -isprinted whenever the comparison indicates the video amplitude is at oneof the contour levels.

Scale expansion for low level signals is accomplished by amplifying thevideo to obtain a signal whose strength is increased by a precisefactor. The staircase waveform is compared with the amplified videosignal in a separate detector that emits a pulse when the signals are ofequal amplitude. A switching arrangement is employed which alternatelypermits signals from the normal detector and the scale expansiondetector to be passed to a device which determines whether there iscoincidence with a signal from the logic matrix. In effect, the videosignal is digitized alternately on the normal scale and the expandedscale. The expanded scale provides better accuracy of quantization forlow level signals.

The arrangement of the invention, its construction, and its modes ofoperation can be more fully understood from the following exposition,when considered in conjunction with the accompanying drawings in which:

FIG. l schematically depicts the arrangement of the invention;

FIG. 2 shows the arrangement of magnetic heads around the periphery ofthe memory disk;

FIG. 3 shows the type of spectrum analysis chart produced by theinvention;

FIG. 4 illustrates the memory disk and the print out mechanism and thecontrols associated with those mechanisms;

FIG. 5 shows the components included within the stylus control generatorof FIG. 4;

FIG. 6 illustrates the scheme for quantizing the video signal andproducing contour pulses at discrete amplitude levels;

FIG. 7 sholws the staircase waveform generated by the digital to analogconverter of FIG. 6;

FIG. 8 tabulates contour levels relative to the count in the counter ofFIG. 6 and the N signal from the flipop;

FIGS. 9A to 9D illustrate linear and logarithmically related contourlevels and the sequence of pulses that are produced by the contourgenerator;

FIG. 10 is a schematic diagram of a crossover detector that may beemployed in the invention;

FIG. l1 illustrates the negative resistance characteristic curve of atunnel diode;

FIG. 1-2 depicts the arrangement of the controls in the synchronizationsystem;

FIGS. 13, 14, and 15 show the relative positions of the two rotatingmembers while synchronization is being obtained;

FIG. 16 tabulates the operation of the synchronization system.

The scheme of the invention is depicted in FIG. 1. The message to beanalyzed is, for the purpose of this exposition, assumed to be a trainof complex waves having frequency components in the part of the spectrumextending from 50 cycles per second to 20 kilocycles per second. Themessage is recorded as magnetic signals upon a disk 1 which acts as thememory for the system. As shown in FIG. 2, three transducers or headsare arranged around the periphery of the memory disk 1. The memory diskrotates in the direction indicated by the arrow in FIG. 2. Record head 2is employed to place the message, as magnetic signals, around theperiphery of the memory disk. To insure that the recording track iscleared of signals before a new message is placed on the track by therecord head, an erase head 3 is energized during the recordation of themessage. From the direction of rotation of the memory disk (FIG. 2), itis apparent that the erase head is positioned to erase the track,shortly before the erased track passes to the record head. Theseparation between the erase head the record head is of interest becausethat separation makes a portion of the track unusable as a memory store.A playback head 4 is utilized to read the message recorded upon thememory disk. The functions of the playback head and the record head canbe accomplished by a single transducer, but it is preferred to useseparate mechanisms.

The magnetic memory disk 1, as depicted in FIG. 1, is rotated by a servocontrolled drive mechanism 5 at a constant speed while the message isrecorded upon the disk. The speed at which the disk turns duringrecording can be set to accommdate messages of different length. Thatis, a message whose duration is 1, 2, or 4 seconds can, for example, berecorded upon the periphery of the disk by setting the speed of rotationso that the entire message is recorded during one revolution of thedisk. While recording, the erase head is energized by an A.C. signalfrom oscillator 6 to remove signals from the track on the memory disk.Oscillator 6, as is customary in high fidelity magnetic recording, alsosupplies an A.C. bias signal for the recording head. The A.C. biassignal is preferably of the same frequency as the A.C. signal suppliedto the erase head and is at least several times higher than thefrequency of the input signal current. The input signal, which mayitself be obtained from a recording, is, when necessary, increased instrength by an amplifier 7. The amplified signal is combined with thebias signal in a mixer 8 whose output is applied to the record head. Thelevel of the input signal is adjusted to insure that the signal isrecorded with fidelity upon the memory disk.

Upon spectral analysis of the message recorded on the memory disk 1,there is produced by the print-out mechanism 9 a type of display that issimilar to a topographic map. The X and Y coordinates of the spectralanalysis map are, respectively, time and frequency and the amplitude,which is analogous to topographical altitude, is represented by a set ofcontour lines. Each contour line is a closed loop and represents adiscrete amplitude level. The contour lines may be used to representlinearly or logarithmically related amplitude levels. yIn addition tothe contour lines, the spectral analysis map has gradations of tone toindicate amplitude in a qualitative manner. That is, amplitude is moreaccurately represented by the contour lines than by the gradation intone of the mapf The gradations of tone show whether the amplitude isrising or falling while the contour lines mark discrete levels ofamplitude. The spectrum analysis map is made upon electrosensitive paperthat is wrapped around a drum in the print-out mechanism 9. The drumdoes not rotate during generation of the map and the display can beobserved as it is generated by a stylus 10 that rotates around the drum.The drum is, however, shifted while the display is generated so that thepath traced by the stylus upon the paper is a tightly coiled helix. Theavailability to Iview of the display as it is generated is a conveniencefeature of some importance as it permits the operator to evaluate theadequacy of the presentation without waiting until the map is completed.A rudimentary map" of the type produced by the print out mechanism isshown in FIG. 3. Time is indicated along the horizontal dimension andfrequency is indicated along the vertical dimension. Frequency markersare produced upon the map by the print-out mechanism. Those markers maybe spaced every 500 cycles, for example, and each marker extends acrossthe chart. The sets of contour lines are formed by closed loops and eachcontour line marks a specific amplitude level of the frequencycomponents. In a set where contour line 11 represents the rst amplitude,the second level is represented by the next contour line 12, the thirdamplitude level is represented by the immediately adjacent contour line13, and so on. The zones between the contour lines are shaded andthereby indicate whether the amplitude is increasing or decreasing.Taking the normal shade of the electrosensitive paper as the datum, andassuming that the datum represents zero amplitude, then the zonesbetween the contour lines become increasingly darker in shade as theamplitude rises and, as a corollary, become increasingly lighter inshade as the amplitude falls. To obtain an accurate estimate ofamplitude at any point on the chart, the number of contour lines thatmust be crossed, proceeding from the datum into increasingly darkerzones, are counted to determine the amplitude level of the contour lineclosest to that point. As amplitude is related to power, the powercontent in the frequency components of the analyzed complex waves is, ineffect, displayed upon the chart in a manner depicting the variation intime of that power and its distribution among the frequency components.

The electrosensitive paper 25, indicated in FIG. 4, is wrapped aroundthe drum 26 in the print out mechanism in a manner which forms a seam27. As it is not desired to write over the seam, the stylus, during thegeneration of the spectrum analysis chart is made to pass over the seamwhile the unusable part of the recording track on the memory disk isscanned by the playback head. The seam, therefore, defines the left andright borders of the chart. Before generating the spectrum analysischart, the position of the stylus with respect to the seam is made tocorrespond with the position of the end of the recorded message withrespect to the playback head to insure that the stylus will pass overthe seam at the time the blank portion of the recording track is scannedby the playback head. After the position of the stylus is brought intothe desired correspondence with the recorded message, the stylus andmemory disk are driven in synchronisml by the servo controlled driver 5to cause the stylus to circle the drum once for each complete revolutionof the memory disk.

When it is desired to have the machine write the spectrum analysischart, the speed of the memory disk is increased to cause the disk toturn five times faster than it turned when the message was recorded. Asthe stylus during the write operation is driven in synchronism with thememory disk, the speed of the stylus is also increased correspondingly.By increasing the speed of the memory disk, the signal frequenciesrecorded upon that disk are translated upward in frequency by a factorequivalent to the increase in speed. Thus, a signal recorded as having50 cycles per second becomes, upon a vefold increase in rotation of thememory disk, a 250 cycle per second signal; similarly, a signal recordedat 20 kc. is translated upwardly to 100 kc. The signals obtained fromthe playback head, during the write operation, are therefore translatedin frequency. The output of the playback head is applied to an amplifier14 and the amplified signals are coupled to a balanced modulator 15.That modulator also receives an input from a voltage controlledoscillator 16. The frequency of oscillator 16 is controlled by a signalderived from the print-out mechanism to cause the oscillator to becontinuously -varied over a selected frequency range in consonance withthe shifting of the drum. That is, as the position of the drum isshifted relative to the stylus, the frequency of oscillator 16 isconcurrently changed so that by the time the drum has been completelyshifted the oscillator has been swept through the selected range. Thechange in frequency of the voltage controlled oscillator is very gradualand permits the stylus t-o make about 100 revolutions per inch of axialdrum movement during the frequency sweep. Thus, the change in frequencyof the oscillator that occurs during one revolution of the stylus isquite small.

The lower sideband output of the balanced modulator contains thosefrequencies that are the difference between the frequency of the voltagecontrolled oscillator and the frequencies of the signals obtained fromthe playback amplifier. Because the frequency of the voltage controlledoscillator is continuously changed as the oscillator sweeps through itsrange, the effect is to shift the difference between each frequency inthe playback signal fsm and the oscillator frequency fvco. For example,assuming the playback signal fsig has a frequency component of 2() kHz.and the voltage controlled oscillator sweeps from 555 kHZ. to 455 kHz.,the difference frequency, which initially is 535 kHz., is swept from 535to 435 kHz. When the oscillators frequency is 475 kHz., the differencefrequency is 455 kHz. The effect of the frequency sweep of the voltagec-ontrolled oscillator is to cause the lower sideband to beprogressively shifted along the frequency axis,

The ouput of the balanced modulator is applied to a filter 17 having abandwidth that is extremely narrow compared to the frequency bandoccupied by the translated signals o-btained from the playback head. Forexample, the translated signals in the lower sideband may extend over aband of 100 kHz., Whereas the band of the filter may be 20() cyclesWide, To provide versatility, filters having bandwidths of 500i cyclesor 1500 cycles may also be provided to allow the operator to select thefilter bandwidth that is best for his purpose. The mean frequency offilter 17 is, for example, 455 kHz. and that filter acts as a fixednarrow window for viewing the output of modulator 15, The frequencysweep of the voltage controlled oscillator causes the output of themodulator to sweep lby the window. The amplitude of the signaltransmitted through the filter 17 is directly related to the amplitudeof that portion of the modulators output that is within the bandwidth ofthe filter. At each rotation of the memory disk, a different portion ofthe modulators output is brought within the bandwidth of the filter.That is, the lower sideband of the modulators ouput is, effectively,slowly drawn past the narrow spectral window presented by the filter.

The output of filter 17 is passed into a demodulator 18 to obtain aVideo signal whose variations correspond to the amplitude envelope ofthe filters output. The video output of the demodulator is quantized byan analog to digital converter 19 whose output is applied to a contourgenerator 20. The contour generator is a switching matrix which emits ap-ulse whenever the analog signal from demodulator 18 reaches any one ofa number of discrete amplitude levels. A selector 21 permits thosediscrete amplitude levels to be linearly or logarithmically related. InFIG. 9A, for example, seven amplitude levels are indicated by thehorizontal broken lines. The contour generator emits a pulse, asindicated in FIG. 9B, whenever the video signal is at any one of thoseseven levels. In FIG. 9A, the amplitude levels are indicated to belinearly spaced. Because logarithmically related contours may be moredesirable, the conto-ur levels can be logarithmically spaced asindicated in FIG. 9C. As shown in FIG. 9D, the sequence of pulse emittedby the contour generator is, of course, different, because of the timeat which the video signal reaches the logarithmically related levels. Itis obvious that the amplitude levels can be set in any relationship thatis wanted and need not be restricted to linear or logarithmic relations.The machine may have any desired number of discrete amplitude levels atwhich contour generator 20` emits a pulse. For each discrete amplitudelevel at which a pulse is emitted, a contour line is produced upon thechart. A large number of discrete amplitude levels results in crowdingtogether of the contour lines and in some applications it may bedesirable to eliminate some of the contour lines. The contour levelinhibit control 22 permits any of the contour lines to be eliminated lbypreventing contour generator 20 from emitting a pulse when the analogsignal reaches a specific amplitude level. For example, inhibit control22 can be set to prevent the contour generator from emitting pulses whenthe analog signal in FIG. 9A passes through the third and fifth levels.Thus, the apparatus which normally provides seven contour levels on thechart, now indicates only five conto-ur levels.

The analog output of demodulator 18 and the pulse output of the contourgenerator are applied as inputs to a video shaper 23. The video shaperconverts the input signals to signals suitable for application to thestylus driver 24. That is, the shades produced upon the electrosensitivepaper depend upon the amplitude of the voltage applied to the stylus.The shading characteristic of the paper is not, however, linearlyrelated to the voltage applied to the stylus. The signals from thedemodulator 18 and the contour generator pulses must, to preservefidelity, be matched to the characteristic of the electrosensitivepaper. The video Shaper changes the shape of its input signals toproduce the proper shading upon the paper.

Referring now to FIG. 4, the electrosensitive paper 25 is Wrapped arounddrum 26 in a manner forming a seam 27 where the ends of the Ipaper abut.To more securely retain the paper upon the drum, the ends of the Ipapermay be clamped against the drum by a spline. In order that the splineshall not protrude above the surface of the drum, the drum may beprovided with a groove which receives the spline so that the surface ofthe spline forms a continuation of the drums cylindrical surface. Drum26 is supported upon a standard 28 which permits the drum to moveaxially; that is, the drum is able to move up and down upon the standard28. The drum does not rotate while a chart is being produced by thestylus 10, but is moved translationally upon the standard by a threadedsleeve 29 which is in engagement with a lead screw 30.

Stylus 10 is fixed to a ring gear 31 that surrounds and is concentricwith the drum. Rotation of ring gear 31 causes the stylus to move aroundthe drum in a fixed circular path. Ring gear 31 is driven by a gear 32and the ring gear, in turn, drives a gear 33 which carries a pin 34.Gears 31, 32 and 33 are of the same diameter and have the same number ofteeth so that each rotation of the drive gear causes the driven gear tomake one turn. Pin 34 interrupts the beam between a source ofillumination 35 and a photocell 36 once during each rotation of gear 31.Gear 33 can be eliminated and pin 34 can be carried by either gear 31 orgear 32, if desired. Because the drum does not rotate during writing ofthe chart, seam 27 remains angularly fixed and, consequently, theposition of pin 34 relative to the light beam is related to the positionof stylus 10 relative to the seam.

The power for rotating the stylus and for causing the drum to movetranslationally during the write operation is provided by a servo motor37. When clutch 38 is engaged, the servo motor is coupled to gear 32 anddrives ring gear 31 through gear 32. During the write operation, clutch39 is also engaged to cause the servo motor to drive lead screw 30through a train of gears comprised by gears 40 to 44. The gearing isarranged to cause the lead screw to move the drum upward a shortdistance while the stylus makes one revolution around the drum. The pathtraced out upon the paper by the stylus is, therefore, a tightly coiledheliX.

The servo motor directly drives magnetic memory disk 1 upon which themessage to be analyzed has been recorded. The record head 2 is connectedto the output of mixer 8 which receives its inputs from amplifier 7 andbias oscillator `6. Erase head 3 is connected to oscillator 6 whichsupplies the excitation for erasing the signals on the memory disk.Playback head 4 has its output delivered to a stylus control generator45. A record switch 46 is provided upon a control panel 47 to controlthe application of signals to the record head. Upon actuation of switch46, amplifier 7 and oscillator 6 are brought into operation and emitsignals to the miXer and to the erase head. A speed selector 48 isprovided on the control -panel to permit messages of various lengths tobe recorded upon the memory disk. The speed selector controls the speedof rotation of the memory disk by governing the speed of the servomotor.

A reference disk 49 is directly driven by the servo motor andconsequently rotates in synchronism with the memory disk. A signalhaving 5000 cycles is magnetically recorded around the periphery of thereference disk and a transducer 50 is positioned to read the recordedreference signals. Thus for each complete revolution of the referencedisk, the transducer emits a signal having 5000 cycles. While memorydisk 1 and reference disk 49 are depicted as .separate devices, it isobvious that two signal tracks on a single disk may be employed in theirstead. Signals from transducer 50 are transmitted to amplifier 53 inmotor `control system 51 and that amplifier emits a pulse for each cycleread from the reference disk. The pulses are passed into a discriminator54 whose output is coupled to a comparator 56. The pulse discriminator54 emits a D.C. signal which is a function of the speed of rotation ofthe reference disk and, therefore, of the `speed of the servo motor. Theoutput of the discriminator is compared with a D C. signal from a source52. The magnitude of the D.C. signal from source 52 is controlled by thespeed selector 48 in panel 47 and the magnitude of that signaldetermines the speed of the servo motor. Comparator 56 emits an errorsignal to motor amplifier 57 which causes that amplifier to increase ordecrease the power applied to the servo motor to meet the speed calledfor by the speed selector. Motor amplifier 57 is energized from thecontrol panel whenever record switch 46, playback switch 58, analyzeswitch 59, or write switch 60 are actuated and the motor amplifier isdeenergized by actuation of stop switch `61.

After the message is recorded upon the memory disk, playback switch 58in the control panel is actuated. The memory disk then is driven at thesame speed at which the recording was made, but the record and eraseheads are now unenergized and the signals on the memory disk are read bythe playback head 4. The output of the playback head, as indicated inFIG. is impressed, through a preamplifier 62, upon playback amplifier14. The output 0f the playback amplifier is coupled into a speakeramplifier 63 which drives a speaker 64 or energizes a pair of phones 65.The operator is able to determine, upon playback, whether the messagehas been properly recorded.

Actuation of playback switch 58 (FIG. 4) also initiates operation of asynchronizing circuit 66 which brings about an adjustment in theposition of stylus to cause it to pass over the seam 27 at the time theblank portion of the memory disk is being read by the playback head.After the position 0f the stylus is -appropriately adjusted, the

stylus and the memory disk are caused to rotate in synchronism.Subsequently, the analyze switch 59 is actauted to place the apparatusin a mode which permits it to be programmed. Upon actuation of analyzeswitch 59, the speed selector causes source 52 in the motor controlsystem to emit a signal to comparator circuit 56 which increases thespeed of the memory disk and the stylus by a factor of five. Thatincrease in speed results in an upward translation of the frequencies inthe recorded message. During the analyze mode, the appropriate bandwidthfor filter 17 is selected, the contour selector 21 is set to provideeither logarithmic or linear spacing of the contour levels and thecontour level control 22 is set to suppress undesired contour lines.While in the analyze mode, the video signal derived from the playbackhead 4 is monitored to ascertain its highest level and the gain ofplayback amplifier 14 is adjusted to insure that the signal does notexceed the amplitude of the highest level contour line.

The voltage controlled oscillator is capable of being swept over a rangeextending from 555 to 455 kHz. during the production of a frequencyspectrum chart. However, the control voltage applied to oscillator 16can be regulated during the analyze mode to cause the oscillator tosweep across a selected part of that range. For example, the controlvoltage may cause the oscillator to sweep from 555 to 505 kHz. duringthe generation of the chart. The control voltage for oscillator 16 isobtained from the wiper of a potentiometer in the voltage controloscillator drive unit 67 depicted in FIG. 4. By changing the voltageimpressed upon the potentiometer, the frequency sweep of oscillator 16is changed. Because the range over which the oscillator 16 sweeps can beselected, it is highly desirable to have frequency markers on the chartto indicate the range of frequencies that are included on the chart. Afrequency mark generator 68 is shown in FIG. 5 which emits markersignals at terminal 69. When those signals are impressed upon stylus 10,they cause the stylus to mark lines across the chart, as indicated bythe frequency markers in FIG. 3. The frequency mark generator iscontrolled by a digital voltmeter 70. The output voltage of the VCOdrive 67 (FIG. 4) is applied to voltmeter 70 and to oscillator 16. Asthe voltage from the VCO drive controls the frequency of oscillator 16,the voltmeter 70 can be calibrated to read frequency. At particularfrequencies, the voltmeter causes generator 68 to emit a marking signal.For example, the generator may emit `marking signals at 500 Hz.intervals. For versasility, the output of frequency mark generator `68may be gated to cause the marking signals to appear at 1000 Hz.intervals or less often, depending upon the range over which oscillator16 is permitted to sweep during generation of the spectrum analysischart.

Before commencing generation of the chart, the drum is positioned tohave the stylus near the top of the electrosensitive paper. To permitthe drum to be rapidly brought into that position, a fast up-down motor71 (FIG. 4) is provided which drives the lead screw 30 through gears 72,73, and 74. When the drum approaches the top or bottom of its travel,whether driven by servo motor 37 or fast motor 71, the sleeve 29 trips aswitch which cuts off the motor and causes brakes 75 and 97 to beapplied, thereby preventing the drum from overrunning the permissiblelimit of travel.

After the apparatus has been programmed and with the drum in theappropriate initial position, the write switch 60 is actuated to causethe spectrum analysis chart to be produced. During the write phase, thememory disk rotates at five times the speed at which the message wasrecorded and the message is repetitively read lby playback head 4 (FIGS.1 and 2). Actuation of write switch 60 (FIG. 4) applies a signal to thestylus control switch 76 which places that switch in a conditionpermitting signals from the stylus control generator 45 to betransmitted to the stylus. For reasons that appear later clutch 77 is inengagement only in the playback mode during synchronization and is,therefore, disengaged during the record, analyze, and write modes. Uponactuation of the write switch, a signal is emitted to relay 55 whichcauses solenoid 39A to be energized. Solenoid 39A controls clutch 39 andupon being energized, that solenoid causes clutch 39 to engage.Engagement of clutch 39 causes the drurn to be slowly raised as sleeve29 progresses up the lead screw 30 while the stylus circles the slowlymoving drum.

The signals produced in playback head 4 during each rotation of thememory disk are applied to stylus control generator 45. The componentswhich make up the stylus control generator are shown in FIG. 5,excluding the speaker amplifier 63, the speaker 64 and phones 65. Thesignals from the playback head, after being amplified in preamplifier 62and playback amplifier 14 are impressed upon balanced modulator 15. Theoutput from the slowly sweeping oscillator 16 is also applied to thebalanced modulator. The modulators output is applied as the input tofilter 17 which constitutes a narrow frequency window. The output offilter 17 is applied to an IF amplifier 78 which provides the input fordemodulator 18. The output of demodulator 18, shown as waveform 79 inFIG. l, is termed the video signal. The video signal is applied to theanalog to digital converter 19 and to the Shaper 23 which provides theoutput for stylus driver 24. The signals emitted by the stylus driverare, when switch 76 (FIG. 4) is in the appropriate condition, applied tothe stylus and cause that stylus to write upon the electro-sensitivepaper 25. As indicated in FIG. l, the output of stylus driver 24 is acomposite signal 80 which has a shaped video component for causing thestylus to shade the chart and has a contour pulse component. The contourpulses are of an amplitude that causes the stylus to be energized atfull intensity and mark the paper with its darkest shade. The contourlines are thereby readily distinguished from the shades due to the videocomponent.

The video signal from demodulator 18 is quantized by the apparatus shownin FIG. 6. A pulse generator 81 is employed as a clock which drives theIbinary counter 82. The periodic pulses emitted by the clock `cause thecounter to repetitively count through a sequence of binary numbers. Forexample, where the binary counter has six stages, the counter countsfrom to 63 and then, on the next pulse from the clock returns to 0 tobegin the sequence again. On each sixty-fourth clock pulse, the counteroverfiows and returns to 0. When the counter overflows it transmits atriggering signal to flip-flop 83 which causes that flip-flop to changestate. That is, regardless of which of the two stable states thefiip-fiop is in initially, the flip-flop changes to its other stablestate. Flip-flop therefore changes its state whenever the countercompletes its sequence.

The stages of binary counter 82 are connected in parallel to a digitalto analog converter 84 which emits an analog signal to crossoverdetectors 85 and 86. Because converter 84 converts the digital output ofcounter 82 to an equivalent voltage value, the voltage value increasesby one unit for each unit increase of the count in the counter. Theanalog signal emitted by converter 84 is, therefore, a voltage havingsixty-four steps, as indicated in FIG. 7. That stepped voltage waveformis repetitively emitted by the converter because the counter continuesto repeat its sequence in response to the pulses continually emitted `bythe clock. Compared to fiuctuations in the video signal, each staircasewaveform is of short duration. That is, because the staircase waveformis generated very rapidly, the video signal can, during the existence ofone staircase waveform, be considered to change very slowly.

The video signal and the staircase waveform are lapplied as inputs tocrossover detector 85. When the amplitude of the staircase waveform fromconverter 84 exceeds the amplitude of the video signal by one step orless, detector 85 emits a pulse signal to switch 87. The staircasewaveform from converter 84 is simultaneously applied to crossoverdetector 86 which receives the video signal after it has been increasedn strength by amplifier 88. Because of amplifier 88 the video signalapplied to detector 86 is eight times greater than the video signalapplied to detector 85. Crossover detector 86 emits a pulse signal toswitch 87 when the staircase waveform equals or exceeds the videosignal.

Switch 87 is controlled by fiip-flop 83. When the fiipflop is in onestable state, it couples the output of detector to AND gate 89; when theflip-flop is in its other stable state, it couples the output ofdetector 86 to the AND gate. The switch prevents both detectors frombeing coupled to the AND gate at the same time. Because flip-fiop 83changes from one state to another each time counter 82 completes asequence of counts, switch 87 alternately connects one crossoverdetector and then the other to the AND gate. Where detector 85 iscoupled to the AND gate for the duration of one staircase waveform, thendetector 86 is coupled to the AND gate during the occurrence of the nextstaircase waveform. As the staircase waveforms are generated in rapidsuccession, the detectors are alternately connected by switch 87 to theAND gate.

AND gate 89 has one of its inputs connected to logic matrix 90. Thelogic matrix may be a conventional switching matrix which receives itsinputs from the normal and complementary outputs of the stages in binarycounter 82.. In addition the switching matrix receives :an input fromflip-flop 83 which, for convenience, is designated the N input. The Ninput can be either a binary ONE or a binary ZERO, depending upon thestate of flip-op 83. The fiip-fiop, when in the state which causesswitch 87 to couple detector 86 to AND gate 89, emits a binary ZERO. Asa corollary, when detector 85 is coupled by the switch to the AND gate,the flip-flop is in the state where the N output is a binary ONE.

Logic matrix is arranged to emit an energizing input to AND gate 89whenever the count in binary counter 82 reaches a value which has beenselected as one of the contour levels. The logic matrix may be in twosections, one of which is used when the contour levels that rareemployed are logarithmically related and the other section of the matrixbeing used when the contour levels that are used are linearly related.The section of the matrix that is employed is chosen through contourselector 21 (FIG. 1) which provides an enabling signal to the section ofthe logic matrix that is selected. Where a linear relationship isselected, the logic matrix, for example, may emit an energizing input tothe AND gate 89 when the count reaches 8, 16, 24, 32, 40, etc. That is,`a count of 8 in the binary counter determines the first contour level,the count of 16 in the binary counterdetermines the second contourlevel, the count of 24 determines the third contour level, and so on. Inthe absence of an energizing signal from the logic matrix, AND gate 89is inhibited. AND gate 89 emits an output pulse to shaper 23 (FIG. l)only when both its inputs are simultaneously energized. That is, ANDgate 89 emits a signal only if a pulse from detector 85 or detector 86is applied to the input of the AND gate while an energizing signal isbeing emitted by the logic matrix.

Amplifier 88 (FIG. 6) effectively causes an expansion of the lowerregion of the staircase waveform shown in FIG. 7. A video signal fromthe demodulator which falls within the low range is, in crossovervdetector 85 compared with not more than the first eight steps of thewaveform. After being amplified eightfold by amplifier 88, the videosignal is compared in detector 86 against a maximum of 64 steps. Theamplifier 88 therefore provides a factor of eight scale expansion forlow level signals from the demodulator 18 (FIG. l). For low levelsignals, both detectors 85 and 86 emit pulses during the existence ofthe same staircase waveform. The pulse from detector 85 or detector 86will pass through switch 87, depending upon the state of flip-flop 83.Because of the N signal emitted by the Hip-flop to the logic matrix, ANDgate 89 will be inhibited if the pulse from detector 85 passes throughthe switch;

if the pulses that pass through the gate are from detector 86, the ANDgate will be enabled by an energizing signal from the logic matrix ifthe count in the counter is at one of the contour values. That is, forlow level video signals, only pulses from detector 86 can `cause anoutput from the AND gate.

Where the normal video signal is above the low range indicated in FIG.7, then the amplified video signal, whose level has been increasedeightfold, is above the highest step in the staircase waveform. Thestaircase waveform, in that situation, never attains the amplitude ofthe amplified video signal and detector 86 does not then emit a pulse.Hence, for normal video signals that are above the low range, onlydetector 8S is able to emita pulse.

FIG. 8 tabulates logarithmically related contour levels with respect tothe decimal value of the count in counter 82 and the value of the signalN emitted by fiip-fiop 83. In the FIG. 8 table, it is assumed that thecounter uses the standard binary code. The stages of the counter :areindicated under the columns headed 20, 21, 22 25, and the output of astage is indiacted as being either a binary ONE or a binary ZERO. The Nsignal indicates whether the normal or the expanded scale is used. WhenN is a binary ZERO, the expanded scale is used; when N is a binary ONE,the normal scale is used. The first `contour level, for example, isdetermined by a count of eight when the expanded scale is used. Thefourth contour level is also determined by a count of eight when thenormal scale is used. When the counter reaches 1a count of eight, the 23stage of the counter emits a binary ONE signal while all the otherstages emit binary ZERO signals. The logic matrix, in response to thatoutput of the counter emits an energizing signal to AND gate 89 (FIG.6). If during that energizing signal, a pulse is emitted by detector 85and is transmitted through the switch 87 to AND gate 89, the videosignal is at the fourth contour level. If during that energizing signalinstead of a pulse from detector 85, a pulse is emitted by detector 86and is transmitted through switch 87 to AND gate 89, then the videosignal is at the first contour level. It is necessary to be able todistinguish between a pulse signifying the fourth amplitude level and 1apulse signifying the first amplitude level where it is required that theapparatus be capable of suppressing `any desired contour. The N signalfrom fiip-flop 83 provides a convenient means of distinguishing betweenthose amplitude levels.

An electrical circuit suitable for use as a crossover detector isdepicted in FIG. 10. The circuit utilizes a tunnel diode TD1 that is inseries with a resistor Rs. The tunnel diode is connected by resistor R2to a terminal 91 at which a voltage --Vcc is impressed. The tunnel diodeis connected between the base and emitter of transistor Q1 and thetunnel diode thereby shunts the input to the transistor. For expositorypurposes, the transistor Q1 is indicated to be of the NPN type and itscollector is coupled by resistor R1 to a terminal 92 at which a positivevoltage -l-Voc is impressed. The staircase waveform, derived from theanalog to digital converter (FIG. 6), is applied at terminal `93. Theemitter of the transistor is connected to terminal 94 at which the videosignal is impressed.

The characteristic curve appearing in FIG. ll depicts the manner inwhich the current fiow through the tunnel diode varies with the voltageimpressed across the diode. Current is plotted along the ordinate andvoltage is plotted along the abscissa. The series resistor Rs determinesthe load line 95 which intersects the characteristic curve at points aand b. The high conductance state of the diode occurs when the voltageimpressed across the tunnel diode Va; the low conductance state of thediode occurs at the voltage Vb.

Assuming the video signal Es applied at terminal 94 to be an essentiallyunvarying signal in relation to the rapidly changing staircase waveformEL, the tunnel diode is reversely biased when the amplitude of EL isless than the Es amplitude. The tunnel diode, when reversely biased, is

in its nonconductive state. Because transistor Q1 is also reverselybiased by those signals, the transistor is cutoff and the voltageappearing at output terminal 96 is -l-Vcc. As the staircase amplituderises and becomes greater than Es but less than Va, the current flow Idthrough the tunnel diode is much greater than the current Ib flowing inthe base of the transistor. When the amplitude of E1, rises and reachesVa, the tunnel diode very rapidly switches from its high conductancestate to its low conductance state. `In the low conductance state of thetunnel diode, the base current Ib of the transistor exceeds the diodecurrent Id. Because the change from high conduction to low conductionoccurs very rapidly in the tunnel diode, transistor Q1 is suddenlybrought into conduction, causing the output voltage 'E0 at terminal 96to drop abruptly. Thereafter as the amplitude of the staircase continuesto increase, the tunnel diode acts as a conventional diode. The circuitis reset very rapidly when the staircase waveform drops abruptly at theend of the counters sequence.

The synchronizing circuit 66 of FIG. 4 is shown in more detail in FIG.l2. The purpose of the synchronization circuit is to bring about anadjustment in the position of stylus 10 (FIG. 4) to cause that stylus topass over the seam 27 at the time the blank portion of the memory diskis read by the playback head. By synchronizing, it is here meant thebringing of two rotating bodies into a desired angular relationship.This is accomplished by synchronizing the rotation of ring gear 31, uponwhich the stylus is carried, with the rotation of memory disk 1 to causethe end of the message on that disk to be at the playback head 4 just asthe stylus reaches the leading edge of the seam. The stylus will thencross the seam while the blank portion of the recording track of disk 1is scanned by the playback head.

In the record mode, clutches 38, 39, and 77 are all disengaged. Upontermination of the record mode, the end of the message is at the erasehead. When entering the playback mode, the position of the end of themessage is known. The initial position of the stylus however is notknown when entering the playback mode and the position of the stylus isfirst ascertained when pin 34 intercepts the light beamed towardphotocell 36. Upon commencement of the playback mode, signals derivedfrom the 5000 cycles recorded upon the reference disk are emitted as atrain of pulses by the amplifier 53 in the motor control system 51.Those pulses are termed sync pulses. Because the reference disk 49 is onthe same shaft as memory disk 1, precisely 5000 pulses are emitted fromamplifier 53 for each rotation of the memory disk.

IUpon actuation of the playback switch 58 (FIG. 4) on the control panel,a signal is emitted to switch 100 in FIG. l2 which causes that switch toapply the D.C. voltage at terminal 101 to clutch relay 102. Switch 100is of the selflatching type and continues to apply the D.C. voltage toclutch relay 102 until switch receives an unlatching signal. Clutchrelay 102 applies the D.C. voltage to one or the other of two solenoids38A or 77A, depending upon whether the clutch relay is latched orunlatched. Solenoid 38A controls the operation of clutch 38 (FIG. 4) andwhen that clutch is engaged stylus 10 is driven together with memorydisk 1. Solenoid 77A controls the operation of clutch 77 (FIG. 4) andwhen clutch 77 is engaged the stylus is driven, through a train ofgears, at one half the rotational rate of the memory disk. Clutch relay102 is arranged, when unlatched, to apply the D.C. voltage to solenoid77A'to cause clutch 77 to engage. Upon being latched, relay 102transfers the D.C. voltage to solenoid 38A, whereupon clutch 38 engagesand clutch 77 disengages. At the start of the playback mode, relay 102is unlatched, having been placed in that condition during the recordmode. The signal from the playback switch which causes switch 100 toapply D.C. voltage to relay 102, therefore, results in energization ofsolenoid 77A and engagement of clutch 77. Consequently, when theplayback switch is actuated, stylus 10 is driven 13 at one half therotational rate of the memory disk.

Clutch relay 102 is coupled to a counter 103 which, upon counting10,0001 pulses, emits a signal that causes relay 102 to latch. The pulseinput to the counter is obtained from a switch 104 that has twopositions. In one position, switch 104 couples all the sync pulsesapplied at terminal 105 to the counter 103; in the other position,switch 104 couples the output of flip-'op 106v is at one half the rateof the pulses impressed at terminal 105. When switch 104 is in theunlatched condition, it connects only terminal S to the input of counter103 and when switch 104 is latched, it connects only the output of theyflip-flop to the input of counter 103. During the record mode, a signalis applied to switch 104 to unlatch that device and the counter 103 isreset to zero.

At the start of the playback mode, all the sync pulses are applied tothe input of counter 103, while the stylus rotates at one half the rateof the lmemory disk. When pin 34 (FIG. 4) interrupts the light beamed tophotocell 36, that photocell emits a signal to ampliiier 107 (FIG. 12)that causes switch 104 to latch. Switch 104, being of the self-latchingtype remains in that state until it receives an unlatching signal. Uponbeing latched, switch 104 permits the pulses emitted from flip-flop 106to be applied to the counter. The counter which formerly was countingthe pulses at their full rate, upon latching of switch 104 counts thepulses at one half their full rate. Upon counting 10,000 pulses, counter103 emits a signal which latches clutch relay 102. The clutch relaythereupon transfers the D C. voltage to solenoid 38A which causesengagement of clutch 38 and disengagement of clutch 7'7. At theengagement of clutch 38, stylus 10 rotates at the same rate as thememory disk and the stylus passes over the seam when the blank portionof the recording track passes by the playback head.

The operation of the synchronizing circuit can be better understood withaid of FIGS. 13, 14, and which show corresponding positions of pin gear33 and the memory disk 1 during successive steps in that operation. Inthose figures all angles are given in radians. At the conclusion of therecord mode the end of the message recorded on the memory disk is at theerase head 3. The end of the message is, for expository purposes,`indicated :by the dot M1 in the gures. The pin 34, carried on gear 33,may, at the beginning of the playback mode, be anywhere relative to theposition of photocell 36 and a position for that pin has beenarbitrarily chosen in FIG. 13. At the initiation of playback, pin 34 isat the angle 0 with respect to the reference line and the photocell 36is xed at the angle qa with respect to the reference line. At the sametime, the end of the message M1 0n the memory disk is at the angle nwith respect to the same reference line. Gear 33 at the beginning ofplayback rotates at 1/2 the rotational rate of the memory disk and allthe sync pulses, derived from the reference disk, are applied totheinput lof the counter (FIG. l2). When, as indicated in FIG. 14, pin 34comes into alignment with the photocell, the signal emitted yby thephotocell causes the pulses applied to the counter to be at 1/2 the fullsync pulse rate. At the time the counter begins the 1/2 rate count, pin34 has moved through an angle 21r-0+ relative to its initial positionwhile the end `of the message M1 has moved through twice that angle,viz., 2[21r-0}]. When the pulse count in the counter reaches 10,000, pin34, as indicated in FIG 15, has moved through an additional angle 2(0)and the memory disk has rotated through an additional angle 4(0-qb). Atthe 10,000 count, the counter causes gear 33 and memory disk 1 to .becoupled together in a manner causing them to rotate in synchronism.Thereafter, pin 34 rotates into alignment with the photocell at the sametime that the end of the message comes into alignment with the erasehead.

FIG. 16 tabulates the position of pin 34, the position of the end of themessage M1, and the count in the counter at the times depicted in FIGS.13, 14, and l5. The position of the end of the message M1 is 41r+o1 l202when synchronization is achieved. As the 4r term means the end of themessage has made two full revolutions (viz, 1r=720), that term maybeignored and the position of M1 relative to the reference line atsynchronization is 'n+20-2. The position of pin 34 relative to thereference line at synchronization is 20-0. If then, the angular positionof pin 34 at synchronization is subtracted from the angular position ofM1 at synchronization, viz., 1;-1-26-255-(20-0) the result gives theangular relation a between the pin and M-1 4and that result is =1r-Ql.That is, the angular difference betwen pin 34 and the end of the mesageM1 when synchronization is achieved, is the angle Further, as 0 does notappear in the equation, the angle a is shown to be independent of thestarting position of pin 34. The angle a is determined only by theinitial position of M1 and the position of photocell 36 relative to thereference line. The position of stylus 10 is related to the position ofthe pin 34 so that adjustment of the position of pin 34 relative to theposition of the end of the message M1, in eifect, also adjusts theposition of the stylus. Indeed, the stylus and the pin can lbe carriedupon the same gear, if desired. Further, the position of the playbackhead 4 is fixed relative to erase head 3, as indicated in FIG. 15.Because those relationships are known, the stylus is made to pass -overthe seam at the time the end of the message reaches playback head 4. Thesynchronizing system computes when the memory disk, which is rotatingtwice as fast as the pin gear, has overtaken that gear by suicientangular rotation to cause the end of the message to be situated in thecorrect angular position relative to the stylus and when that correctrelative position is achieved, locks the memory disk to the pin gear tocause them to rotate together.

Although the pin gear has, for expository reasons, been described asbeing driven at one half the rotational rate yof the memory disk, otherratios of rotation may be employed to attain the same result. If otherratios are used, the reduced rate at which the pulses are fed into thecounter upon command of the photocell signal must also -be altered.Thus, where n is the ratio of the rotational rate of the faster memberrelative to the slower member, then the reduced rate u, at which pulsesare fed to the counter upon command of the photocell signal, `becomesFor example, where the faster member rotates at four times the rate ofthe slower member, the rat-io n=4 and u=% Thus, when the signal from thephotocell is received, the pluses are applied to the counter at threefourths of full sync pulse rate.

In view of the multitude of ways in which the invention can :beembodied, it is not intended that the scope of the invention berestricted to the precise apparatus illustrated in the drawings ordescribed in the exposition. Rather it is intended that the scope of theinvention be delimited by the claims appended hereto and that withinthat scope be included only those structures which in essence utilizethe invention.

What is claimed is:

1. Apparatus for displaying the spectral composition of complex wavesupon a chart, the apparatus comprising a memory device for storing thecomplex waves;

means for repetitively reproducing the complex waves stored in thememory device;

means for selecting in progression the frequency components of thecomplex waves, a dilerent frequency component being selected at eachreproduction of the complex waves;

a chart;

a stylus for writing on the surface of the chart;

means for causing the stylus to trace a different path upon the chart insynchronism with the repetitive reproduction of the complex Waves tocause each path to be related to a different frequency component of thecomplex waves;

means for quantizing each frequency component to obtain the digitalequivalent of the amplitude of the frequency component at a plurality oftimes;

means responsive to signals representing the digital equivalents forgenerating signals causing the sylus to produce contour lines on thechart when the amplitudes of the frequency components are at discretelevels; and

means responsive to variations in the amplitude of the frequencycomponents for causing the stylus to produce marks of graded intensityupon the chart.

2. Apparatus as in claim 1 wherein the means for causing the stylus totrace different paths upon the chart includes a drum around whosesurface the chart is disposed,

means for causing the drum to be axially translated,

and

means for causing the stylus to rotate around the drum while the drum isaxially translated whereby the stylus track upon the chart is a tightlycoiled helix.

3. Apparatus as in claim 2, wherein the memory device for storing thecomplex waves is a magnetic disk, the apparatus further includingReferences Cited UNITED STATES PATENTS 8/ 1947 Potten 12/ 1950 Potter.

8/ 1957 Giacoletto. 12/ 1967 Guro et al. 324--77 WILLIAM C. COOPER,Primary Examiner.

T. TAYLOR, Assistant Examiner.

U.S. Cl. X.R.

